1. Field of the Invention
The present invention relates to a displacement amplification mechanism for a piezoelectric element by the use of a piezoelectric element as a primary drive and particularly such a mechanism improved with respect to accuracy in mechanical configuration.
2. Description of the Prior Art
As shown in FIG. 1, one of mechanical amplification mechanisms constructed in accordance with the prior art comprises a piezoelectric element 1 which is connected at its both end faces to a pair of lever arms 6 through displacement transmitting means, such as hinges 3, for transmitting the produced displacement A of the piezoelectric element to the respective lever arms 6. Each of the lever arms 6 is connected to the corresponding end face of a base plate 4 through each of hinges 5, the base plate having a mounting aperture 4a. The other ends of the lever arms 6 are connected to each other through a beam 14 made of a sheet material which extends in the form of a bridge between the lever arms 6. The beam 14 is held at ends of the lever arms 6 with flat head rivets 8. In the mechanism thus constructed, when an electric voltage is applied to the piezoelectric element 1 to cause a displacement in the direction of A as shown in FIG. 1, the displacement A is transmitted to the respective lever arms 6 through the displacement transmitting means. The displacement A transmitted to each of the lever arms 6 is then amplified at the tip ends of the lever arms 6. The amplified displacement is axially transmitted to the bridge-shaped beam 14 at its opposite ends. The beam 14 is deformed in the direction of B perpendicular to the direction of the displacement applied thereto at the direction of the displacement applied thereto at the opposite ends according to the well known buckling theory. The maximum displacement B occurs at the central portion of the beam 14. When the applied voltage is shut down, the piezoelectric element 1 returns to its original configuration and the central portion of the beam 14 also returns to its original position.
In the prior art mentioned above, for example, if it is assumed that the displacement of the piezoelectric element 1 is equal to 8 .mu.m, the rate of amplification by the lever arm being about four times and the beam being 0.1 mm thickness, 2.6 mm width and 16 mm length, the maximum displacement equal to 180 .mu.m provides the maximum force equal to 35 gf when the displacement is constrained. Since the beam is made of the sheet material, however, the central flat portion of the beam is undesirably curved into an arcuate configuration as the voltage is applied to the piezoelectric element.
Therefore, if the central flat portion of the beam carries a drive such as a magnetic head for VTR dynamic tracking, there are created cracks at the joint between the beam and the central part of the magnetic head.
Another problem in the prior art is that the maximum displacement is reduced 5%-15% when the deformation is suppressed as by joining the drive such as magnetic head to the central flat portion of the beam.